1. Field of the Invention
The present invention concerns the transfer of a liquid, nominally oil, from the ruptured tank(s) of a first ship, which may be an oil tanker or a vessel of any type, to the tank(s) of a second, receiving, vessel, and/or to tank(s) upon the shore, while constantly, and also dynamically, maintaining a partial vacuum in the ullage space of the ruptured tank(s) during the transfer, thereby to minimize spillage though the rupture(s) even as the oil is being transferred. The present invention further concerns the plumbing of a ship's tank containing liquid, nominally oil, in order to facilitate both a normal, and any emergency, evacuation of the liquid contents of the tank, including any emergency evacuation of the partial liquid contents remaining in a ruptured tank.
2. Background of the Invention
With the advent of supertankers, a single oil spill incident can (i) cause significant damage to the environment, (i) disrupt the ecological balance, and (i) cause substantial economic loss. The accident of EXXON VALDEZ is perhaps the worst oil spillage disaster in U.S. history. The EXXON VALDEZ leaked about 240,000 barrels--over 10 million gallons of oil. The economic and environmental cost is estimated to have been over two billion dollars.
When a tank containing liquid, nominally oil, of a ship is ruptured then it is imperative that any remaining liquid within the ruptured tank should be transferred to a secure, unruptured, tank on the same or on another ship, or on shore, as soon as is possible. By doing so, any remaining, unspilled, contents of the ruptured tank are less likely to escape, and to add to any volume of escaped liquids that may already be contaminating the environment. It is always eventually necessary to transfer the oil or other liquid from a ruptured tank even if such liquid is substantially, or totally, retained within the ruptured tank because the rupture must ultimately be patched or repaired, including by dry-docking the ship.
2.1 Related Background to the Present Invention
The predecessor, related, patent applications to the present application teach related inventions for reducing or forsteming any outflow of liquid, such as oil, due to the rupture of a ship's tank. The system, and method, of the related inventions involve the creation, and the subsequent dynamic maintenance, of a partial vacuum in the effected tank or tanks. A partial vacuum below atmospheric pressure is preferably, and initially, created in the ship's tank before any rupture has occurred, and normally after filling of the tank and before disembarkation of the ship. Thereafter the partial vacuum is continuously dynamically maintained in a precise balance responsive to the forces acting on the liquid contents of the tank, which forces change when the tank is ruptured. The dynamically maintained partial vacuum serves to hold the liquid contents of the tank within the tank even if, and when, the tank is ruptured--much in the manner that liquid is held within an inverted glass when the glass is pulled above the liquid level of a reservoir.
If the rupture is below the water line, and on the side of the ship's hull, then surface tension dynamics at the rupture between the tank's interior liquid, nominally oil, and the exterior water will induce a stratified flow, forcing water into the tank through the lower part of the rupture while forcing the liquid oil upward and out of the tank, oppositely to the flow of water. This stratified flow will continue until the water level reaches the top part of the rupture.
In one, preferred, embodiment of the related inventions this stratified flow is stopped because a non-structural barrier, typically a tarpaulin, is placed over the rupture. The barrier is placed over the rupture even as, and while, the partial vacuum is dynamically maintained. The combination of dynamic underpressure control and the non-structural barrier substantially forestalls oil outflow--even below the level of the rupture.
The predecessor, related, patent applications to the present application also teach the maintenance of an inert gas mixture in the ullage spaces above a combustible and vaporizable liquid, nominally oil, in a ship's tank in order to prevent any explosion or combustion. The gas mixture is maintained sufficiently inert so as to prevent combustion even while, and during, the constant, and dynamic, simultaneous maintenance of an underpressure within the tank.
Accordingly, the related applications teach how to substantially contain a liquid, nominally oil, in a ruptured tank--at least temporarily. Once a ship's tank is ruptured, however, its oil, or other liquid, contents must ultimately be transferred to the tank(s) of another vessel, or to other undamaged tanks. The preferred embodiment of the present invention will be seen to accomplish this necessary transfer of oil--while still containing substantially all untransferred oil in the tank(s) of the ruptured tanker or vessel by a simultaneous continuing, and dynamic, maintenance of an underpressure in the ruptured tank(s). This underpressure will be sufficient so as to at all times substantially prevent spillage from the tank through its rupture(s)--even though oil is otherwise, and elsewhere, being intentionally extracted from the ruptured tank(s).
The present invention will thus be seen to deal with the problem, roughly stated, of how to hold oil in a ruptured ship's tank at one outlet from the tank--the rupture--while simultaneously extracting oil from the tank at another outlet--an outlet by which oil may be extracted to an undamaged tank.
Two considerable challenges are presented. First, any interruption in the dynamic maintenance of a partial vacuum in the ullage space of the ruptured tank, even while its oil is being transferred to a safer reservoir, may permit a catastrophic oil spill to occur, or to increase.
Second, to a dynamic underpressure control system (in accordance with the related patent applications) that is trying to hold oil within a ruptured tank, any attempted intentional extraction of oil from the tank appears very much the same as an inadvertent, unintentional, and undesired spillage from the tank.
Interestingly, this second challenge in handling of the liquid, oil, contents of the tank may be compared to the challenge of inerting the gaseous mixture in the ullage space of the tank. This later challenge is met by the system of the aforementioned U.S. patent application Ser. No. 503,712 filed Apr. 3, 1990, for INERT GAS CONTROL IN A SYSTEM TO REDUCE SPILLAGE OF OIL DUE TO RUPTURE OF A SHIP'S TANK.
In the inert gas control system of the predecessor invention the gaseous mixture within the ullage space of a ship's tank must be rendered, and maintained, inert to combustion by putting something, namely inert gas, into the ullage space. This must transpire simultaneously that something else, namely the mixture of inert gases, is being removed from the ullage space in order to create the desired underpressure condition therein. Roughly speaking, two systems and processes must act in opposition to each other in a manner that permits each to accomplish its desired function.
In the system of the present invention the liquid contents of the tank must be removed at a desired outlet from the tank--the mouth of an extraction pipe--simultaneously that the same liquid contents of the tank are precluded, by dynamic underpressure control, from exiting the tank at another outlet to the tank--its rupture. It will subsequently be seen that, in accordance with the present invention, two systems and processes will act upon the liquid contents of the ruptured tank, at least locally at the mouth of the extraction pipe, in opposition to each other. However, because of a relationship that will be seen to be established and maintained between the hydrostatic forces generated, at least locally at the mouth of the extraction pipe, by the two counteracting systems, both systems will be seen to be simultaneously functionally operative for their separate, but related, purposes: holding the oil in the tank at the location of the rupture while extracting the oil at the location of the extraction pipe.
Without immediately explaining the invention, which is directly hereinafter set forth, it might well be considered that several specific questions and challenges would likely have to be addressed, and successfully met, by a system and a method that would permit the selective offloading of oil from a ruptured tank.
First, it would seemingly be important to know exactly where, and/or at what times, oil should be removed (by pumping) from the ruptured tank(s). (In fact, it will prove less critical to know the time(s) of removal.)
Second, the conduits, or pipes, by which the oil is to be removed must be identified. It would seemingly prove useful if the removal conduits were to be, at least in substantial portion, the selfsame existing conduits that are used to fill and/or empty the tank(s).
Third, there must seemingly be some relationship between the negative pressure (suction) forces of the (ullage space underpressure control) system that is attempting to hold oil in the tank(s) versus the like negative pressure forces of the (pumping?) system that is attempting to extract oil from the tank(s). It seems clear that the suction forces of the extraction system must be at least somewhere, and at least regionally, stronger. However, it is not immediately clear where this region, or these regions, are. It is also not clear how much stronger the suction forces of the extraction system should be than the like forces of the retention system.
Finally, there would seemingly be a severe challenge, which will be seen to be successfully met by the present invention, in priming with oil any pump of an extraction system so using a pump when such priming is itself hydrodynamically akin to a spill, meaning that it involves migration Of oil into regions that it does not normally go while resident in an unruptured tank.
2.1 Specific Previous Systems for Emergency Extraction of Ship-borne Liquids, Particularly Oil
Although the best previous systems known to the inventor for the offloading of liquids, nominally oil, from the a ruptured tank(s) of a ship is not deemed to be particularly relevant to the present invention, an overview of such previous systems is useful for understanding the considerable problems faced in evacuating oil from a ruptured tank, and previous approaches to the problems.
U.S. Pat. No. 4,960,347 to Strange for a SHIP-BORNE EMERGENCY OIL CONTAINMENT SYSTEM AND METHOD describes the evolution of a spill of a liquid, nominally oil, from a ruptured ship's tank containing liquid. The SYSTEM contemplates a normally-empty emergency holding tank on the ship. After rupture, a ruptured tank is externally enshrouded by a flexible barrier curtain in order to entrap, at least partially, whatever liquid cargo may have leaked from the ruptured tank. Meanwhile, a water-tight seal is formed at the top of the ruptured tank about an inserted suction intake. The remaining liquid contents of the ruptured tank is pumped through the suction intake to the emergency holding tank until the ruptured tank becomes water-filled to at least the top of the rupture.
The SYSTEM of Strange depends on special equipments--an emergency holding tank of considerable capacity and a flexible barrier curtain--and on a quick response after the occurrence of a rupture. The reason that the emergency holding tank must be on the same ship that incurs the rupture is to permit transfer of oil from a ruptured tank(s) before other support resource could reasonably be expected to arrive. The system and method in accordance with the present invention will be seen (i) to require much less extensive special equipment(s), (ii) to be automatically operative at the time of rupture (and before), and (iii) to be tolerant of such unavoidable delays as will permit other ships into which oil from the ruptured tank(s) will be offloaded to arrive.
Although the workable solution of the present invention will be seen to be straightforward, that such a solution is not obvious may be gauged by the aforementioned Swedish system for which a compatible oil-extraction pumping system has reportedly long been sought.